This invention relates to a method for fabricating a tube, such as an axle-type tube, with inwardly thickened, separated, wall sections.
Axle-type and other similar types of tubular structures, have been formed by extrusion processes which produce wall sections which are inwardly thickened. That is, such tubes have substantially uniform wall thicknesses along their lengths, but at one or more locations along their lengths, the wall thicknesses are increased radially inwardly. Examples of such extrusion processes for providing inwardly thickened wall sections on tubular structures, are disclosed in a number of U.S. patents. Such patents include U.S. Pat. No. 3,837,205 issued Sep. 24, 1974 to Joseph A. Simon for “Process For Cold Forming A Metal Tube With An Inwardly Thickened End.” Another patent, U.S. Pat. No. 3,886,649 issued Jun. 3, 1975 to Joseph A. Simon for a “Process For Cold Forming A Metal Tube With An Inwardly Thickened End,” discloses such an extrusion process. Further patents of Joseph A. Simon which disclose the formation of inwardly thickened portions at the ends of, and within the interior of a tube are: U.S. Pat. No. 4,277,969 issued Jul. 14, 1991 for a “Method Of Cold Forming Tubes With Interior Thicker Wall Sections”; U.S. Pat. No. 4,292,831 issued Oct. 6, 1981 for a “Process For Extruding A Metal Tube With Inwardly Thickened End Portions”; and U.S. Pat. No. 5,320,580 issued Jun. 14, 1994 for a “Lightweight Drive Shaft.”
In the processes disclosed in the foregoing patents, a tubular, short length, metal blank is extruded through a die by a punch which pushes the blank endwise through a die throat. The punch includes an extending mandrel portion which is inserted within the blank and is suitably configured to enable the formation of interior, integral, thickened wall portions within the extruded tube. Such disclosed processes result in elongated tubular members that have provided thickened end portions and thickened interior portions which reinforce the tube in places where needed or for improved strength or for fastening purposes.
These are effective, and relatively economical methods for forming tubes which are strengthened in pre-selected areas while reducing the weight of a tube by providing a thinner wall between the thicker sections. The present invention relates to a method which enables the production of such tubes having interior wall thicknesses more economically.